The present invention relates to a radio access network for a mobile radio communications system and a method for the operation thereof.
Mobile radio communications systems may be broken down into a primary network, in which useful data and signaling data from a multiplicity of terminals is sent over large distances by wire, and a radio access network, also referred to as a RAN, which generally includes a plurality of nodes connected to one or more radio stations. The purpose of these nodes being to convert data received from the terminals into a format suitable for transmission through the primary network and, in the opposite direction, to adapt the format of data received from the primary network for radio transmission and to forward it to the radio station within the transmission area of which the respective terminal is located.
The transmission of useful data and signaling data to the various terminals is a particularly complex task because the radio station within the transmission area of which each of the registered terminals are located at any given time must be known within the radio access network in order for it to be possible to direct data destined for the terminal correctly. Moreover, the mobility of the terminals may necessitate the transmission area in which a given terminal is located to change at any time. The access network must therefore be in a position to change the data route for a terminal at any time while communication is ongoing without any data being lost in the process.
The data to be routed includes both useful data, which is data input by a user via a transmitter terminal, that has a defined meaning outside the mobile radio communications system and is to be received and output by a receiver terminal in, where possible, its original form, and signaling data, which is generated and processed to control internal operations of the mobile radio communications system in connection with the transmission of the useful data. Both types of data have to be exchanged between the radio access network and a terminal communicating therewith.
A distinction may be drawn in the access network between functionalities that are responsible for the transmission of the useful data from a node to a terminal and functionalities that are responsible for the transport of the signaling data. The former are referred to here as transport functionalities or user plane functions and the latter as signaling functionalities or control plane functions. The signaling functionalities include, for example, tasks such as the management of radio resources or line-conducted signaling channels to the primary network, mobility management and the forwarding of signaling information not specific to the radio access network to the primary network.
The signaling functionalities in current GSM and UMTS mobile radio communications standards are held in each case at those physical nodes of the network that also serve as concentrators for the user data traffic for multiple master stations. This node is the base station controller (BSC) in the GSM standard and is known as the serving radio network controller (S—RNC) under UMTS. Each of these network nodes contains both the signaling functionality and the transport functionality for a terminal that is located in the transmission area of a connected base station. Signaling functionality and transport functionality for a given terminal are always held together at the same physical node, so they receive the same physical address.
When an active terminal in an access network of this type leaves the geographical area covered by one node and enters an area covered by another node, both the transport functionality and the signaling functionality have to be shifted to the new node. This operation entails significant signaling activity within the access network, which takes time and reduces the transport capacity of the network for useful data.